Computational study and design of systems for water splitting

Lead by Prof. Sandra Luber

Calculations are an important tool for in-depth investigation of water splitting. They do not only help in interpreting measurements but also provide additional essential information, which may not be easily accessible by experimental data. To this end, we use high level ab initio electronic structure theory and molecular dynamics including density functional theory, wavefunction-based methods, quantum Monte
Carlo as well as ab initio molecular dynamics and molecular mechanics/quantum mechanics. As an interdisciplinary group between (bio-)physics, chemistry and material science, we are interested in a detailed understanding of catalytic processes and related reaction networks including the thorough study of structure and dynamics of catalysts, reaction mechanisms, and sophisticated description of environmental and solvent effects beyond standard static computational approaches. Moreover, development of novel methods for spectroscopy and relevant properties (such as redox potentials) has been in the focus of our research. Such an extensive  understanding is vital for derivation of structure-activity relationships and has been used for informed in silico design of novel catalysts.

In the following we showcase some of our latest research:

In collaboration with the group of Prof. G. R. Patzke, we have studied a series of cobalt-based water oxidation catalysts, which exhibit a cuboidal structure. The latter is not only reminiscent of nature’s oxygen-evolving complex in photosystem II, but also represents the smallest building block of heterogeneous cobalt oxides. In a series of studies, we investigated the thermodynamics and kinetics of possible
reaction pathways and suggested possible design option for improved catalysts. Thereby we discovered unprecedented flexibility of cubanes with respect to several aspects such as the ability to ‘open-up’ revealing a broad range of alternative pathways for water oxidation.

Figure1
Fig. 1: Possible water oxidation pathways of a Cobalt-based cubane (above; published in: ACS Catal. 6 1505) and discovery of open and closed cubane structures (below; published in: ChemSusChem 10 4561).

Besides working with Cobalt catalysts, we have also turned our attention towards Ru-based water oxidation catalysts. We recently helped to rationalize experimental results which suggested that even small modifications to the ligand framework had dramatical effects on the catalytic performance. An in-depth study of the sterics and
electronics of various substituents allowed us to identify the accessibility of a deactivation pathway as the potential source of different catalytic rates observed for distinct ligand-frameworks. Heaving understood the complex reaction network composed of both productive and destructive pathways, we have rationally designed the ligand framework to further improve the catalytic performance.

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Fig. 2: Investigation of water oxidation by a Ru-based catalyst (above; for details, see ChemSusChem 10 4517) and rational design of novel catalysts (below; published in: Dalton Trans. 47 10480).

Another direction of our research concerns spectroscopy for investigation of systems in the gas and condensed phase. Recent examples include the development of efficient approaches for computation of spectra and analysis thereof, based on e.g. perturbation
theory, real time or subsystem methods (density functional theory embedding). This provides valuable additional information for study and design in the field of water splitting in close collaboration with experimental groups.

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Fig. 3: Calculated Resonance Raman excitation profile (above; see J Chem Phys, 149: 174108) and sum frequency generation spectroscopy (below) for study of interfaces (for details see J Phys Chem Lett, 7: 5831, Chimia, 72: 328).